1. Field of the Invention
The present invention relates generally to an apparatus and method for data communication in a wireless communication system. More particularly, the present invention relates to an apparatus and method for periodically allocating uplink resources in a broadband wireless communication system.
2. Description of the Related Art
A number of radio communication technologies have been suggested as candidates for rapid mobile communications. Among those, the Orthogonal Frequency Division Multiplexing (OFDM) scheme is accepted as the most dominant next-generation radio communication technology. In the future, it is anticipated that the OFDM scheme will be adopted to most radio communication technologies. Wireless Metropolitan Area Network (WMAN), which is specified by IEEE 802.16 of 3.5G technology and which is incorporated herein by reference, also adopts the OFDM scheme as a standard.
To transmit data in the uplink in OFDM based broadband wireless communication system, a terminal needs to be allocated uplink resources from a Base Station (BS). The resource is represented in the form of (symbol, subchannel) in two dimensions. The symbol indicates the time and the subchannel indicates the frequency. In general, the basic unit of the uplink resource allocation is a slot, and the amount of the resources is represented as the number of slots.
In the IEEE 802.16 system, the terminal is allocated the uplink resource as follows.
The terminal requests an uplink transmission by sending a ranging code to the BS. The BS sends to the terminal an allocation message (CDMA allocation UL-MAP IE( )) including uplink resource (the number of slots) information allowing it to send a bandwidth request message.
The terminal sends a bandwidth request message to the BS over the slots allocated using the allocation message. The BS allocates the uplink resources to the terminal by analyzing the bandwidth request message, and sends an uplink map message (UL-MAP IE( )) including the allocated resource information to the terminal. Next, the terminal transmits UL data using the resources allocated from the BS.
FIG. 1 depicts a conventional uplink resource allocating method in a broadband wireless communication system.
In FIG. 1, four terminals are assigned five, three, three, and four uplink (UL) slot resources through four UL-MAP IE( ) respectively. Unlike the downlink using the two-dimensional resource allocation method, the uplink allots the resources in one dimension. Each UL-MAP IE( ) contains slot number information (duration information). The terminal recognizes the resources allocated to the other terminals by sequentially interpreting UL-MAP IE( ), and determines a number of slots starting from the start of the allocated slots as its own resources.
Table 1 shows UL-MAP IE( ) for allocating the uplink resource.
TABLE 1UL-MAP IE( ) { CID UIUC Duration Repetition coding indication}
In Table 1, the resource allocating message UL-MAP IE( ) includes Connection IDentifier (CID) information for distinguishing services and terminals, Uplink Interval Usage Code (UIUC) information for designating a modulation scheme, Duration information for indicating a number of allotted slots, and Repetition coding indication information for designating a number of repetition codings.
To allocate the same uplink resources to the four terminals in each frame, four resource allocation messages of FIG. 1 need to be broadcast in every frame. However, in case of a service where the terminal periodically transmits the uplink data (e.g., VoIP service), resources may be unnecessarily wasted as the BS allocates the uplink resources using the resource allocation messages in every frame.
The IEEE 802.16 system maximizes a degree of freedom in the frame constitution by constituting the minimum transmission unit (data burst) of the downlink using one subchannel and one symbol and constituting the minimum transmission unit of the uplink using one slot. However, as the degree of freedom increases, control information to be transmitted also increases. Thus, when a plurality of user data exists within the frame, the information informed to the users using DL-MAP and UL-MAP act as considerable overhead. At the worst, the system throughput may be degraded because of the small amount of allocable resources for the actual traffics.